Method for purification of silica particles, purifier, and purified silica particles

ABSTRACT

[Problems] To provide a treatment method having excellent purification effect, in which impurities having high ionicity in a silica powder can be removed in a short time, a apparatus thereof, and a purified silica powder. 
     [Means for Solving the Problems] A purification method of a silica powder comprises: making a silica powder into a fluid state; contacting a purified gas to the silica powder in the fluid state at high temperature; and thereby removing impurity components of the silica powder. In the method, the silica powder in the fluid state is positioned in a magnetic field region. Further, the silica powder is contacted with the purified gas, while applying voltage to the silica powder by an electric field generated by moving of the silica powder. Preferably, the silica powder in a fluid state is positioned in the magnetic region of 10 gausses or more, and contacted with the purification gas at a temperature of 1000° C. or more.

FIELD OF THE INVENTION

The present invention relates to a purification method of a silicapowder, a purification apparatus thereof, and a purified silica powder.

DESCRIPTION OF THE BACKGROUND ART

A silica powder has been used as a raw material of a filler for aplastic package, such as IC, LSI and the like, or for a raw materialpowder of a quartz glass crucible for pulling up a silicon singlecrystal of a semiconductor material. If impurities are contained inthese silica powders, a semiconductor product is bad influenced so thatthe purified silica powder having few impurities is required.

As for a purification method of the silica powder, for example, JapanesePatent Application Laid Open No. 06-40713 discloses a method including:introducing gas containing chlorine or a chlorine compound into a silicapowder at a temperature of 1000 to 1500° C. so as to fluidize the silicapowder; and dehydrating the fluidized silica powder. Further, JapanesePatent Application Laid Open No. 08-290911 discloses a method including:continuously supplying a quarts powder to a rotary kiln; introducing amixed gas of hydrogen chloride and chlorine into the kiln so as tocontact to the quarts powder; and chloridizing an alkali metal containedin the quarts powders so as to be volatilized and removed. Furthermore,Japanese translation of PCT international application No. 2002-544102discloses a method including: fluidizing a silica powder by chlorinecontaining treatment gas so as to remove metal impurities.

On the other hand, Japanese Patent Kokoku No. 07-14822 discloses anelectrolytic purification method including: applying DC high voltage toa solid quartz glass so as to move alkali metals or the like in theglass on the cathode side; and purifying the quartz glass. Further,Japanese Patent Application Laid Open No. 2004-307222 discloses anexample in which an electrolytic purification is applied to a quartzglass crucible. Furthermore, Japanese Patent Application Laid Open No.2003-119018 discloses a purification method of a quarts powderincluding: applying high voltage to a quartz powder so as to chargeimpurity particles adsorbed on the quartz powder; andelectrostatic-separating the quartz powder.

In the conventional methods for fluidizing a silica powder by apurification gas so as to remove impurities, chlorine gas is used as thepurification gas in many methods, and gas added with hydrogen is alsoused in many methods. However, although the method using hydrogen gascan purify for a short time, there are problems that controlling of gasconcentration is difficult since hydrogen gas has dangerous of anexplosive reaction, and handling of the hydrogen gas is also difficult.Further, it is necessary to set the treatment temperature high such asabout 1300° C. or more in order to increase a reaction rate.

On the other hand, although the method using chlorine gas or hydrogenchloride gas as the purification gas has high effect for removingimpurities, it needs a long time for the purification. In addition, inorder to carry out the purification within a practical time, thepurification temperature must be set a high temperature of 1250° C. ormore so as to obtain high purification efficiency. Thus, there is aproblem in productivity. Further, the conventional electrolyticpurification method also needs long treatment time.

SUMMARY OF THE INVENTION

The present invention solves the above-described problems in theconventional purification method of a silica powder, and an objective ofthe present invention is to provide a treatment method having excellentpurification effect, which enables to remove high ionic impurities in asilica powder for a short time, and a purification apparatus and apurified silica powder.

The present invention relates to a purification method of a silicapowder, a purification apparatus, and a purified silica powder havingthe following constitutions.

(1) A purification method of a silica powder comprising: making a silicapowder into a fluidizing state; contacting a purified gas to the silicapowder in the fluidizing state at high temperature; and removingimpurity components in the silica powder, where silica powder in thefluidizing state is positioned in a magnetic field region and contactedwith the purified gas while applying voltage to the silica powder by anelectric field which is generated by moving the silica powder.

(2) The purification method of a silica powder according to theabove-described (1), where the silica powder in the fluidizing state ispositioned in a magnetic field region of 10 gausses or more, andcontacted with the purified gas at a temperature of 1000° C. or more.

(3) The purification method of the silica powder according to theabove-described (1) or (2), where the purified gas contains any one orboth of a halogen gas and a hydrogen halide gas.

(4) The purification method of a silica powder according to any one ofthe above-described (1) to (3), where the purification temperature isfrom 1000° C. or more to 1300° C. or less.

(5) A purification apparatus of the silica powder comprising: afluidized bed for fluidizing the silica powder or a reaction containerfor receiving the fluidized silica powder; a means for introducing apurified gas into a fluidized bed or a reaction container; a means forheating in the fluidized bed or the reaction container at from 1000° C.to 1300° C.; and a means for forming a magnetic field of 10 gausses ormore in the fluidized bed or the reaction container.

(6) A purification apparatus of the silica powder according to theabove-described (5), where the fluidized bed possesses a function of thereaction container, a lower part of the vertical and cylindrical typefluidized bed is divided by a floor plate having many air hole, thesilica powder is filled on the upper side of the floor plate, apurification gas in-let port is provided at the lower side of the floorplate, and a gas out-let port is provided on the upper side of thefluidized bed;

wherein a heater is provided on an outer periphery of the fluidized bedand the means for forming the magnetic field is provided on an outsideof the heater;wherein the silica powder in the fluidized bed is made to be fluidizingstate by the purification gas introduced from the lower part of thefluidized bed; wherein an inside of the fluidized bed is heated from1000° C. or more to 1300° C. or less; andwherein the magnetic field is formed 10 Gauss or more by the means forforming the magnetic field.

(7) A purified silica powder, wherein impurity components are removed bythe purification method according to any of the above-described (1) to(4).

According to the purification method of the present invention, thesilica powder in a fluid state is positioned within the magnetic fieldregion in 10 gausses or more at a temperature of 1000° C. or more so asto be applied a voltage in an electric field generated by moving thesilica powder, and contacted with the purification gas. Thus, ionicimpurity components contained in the silica powder are induced by theelectric field, diffused onto a powder surface, and easily reacted withthe purification gas. Therefore, high purification effect can beobtained in a short time. The impurity components are reacted with thepurification gas, and removed to an external of the system as gaseouscompound.

BRIEF EXPLANATION OF DRAWINGS

FIG. 1 is a schematic view illustrating a purification apparatus of thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Hereinafter, the present invention will be described particularly withexamples.

The purification method of the present invention is characterized by:making a silica powder into a fluid state; contacting a purified gas tothe silica powder in the fluid state at high temperature; and removingimpurity components of the silica powder, where the silica powder in thefluid state is positioned in a magnetic field region and contacted withthe purified gas, while applying voltage to the silica powder by anelectric field which is generated by moving the silica powder.

Preferably, the purification method of the present invention ischaracterized by: making a silica powder into a fluid state; contactinga purified gas to the silica powder in the fluid state at hightemperature; and removing impurity components of the silica powder,where the silica powder in the fluid state is positioned in a magneticfield region of 10 gausses or more, and contacted with the purified gasat a temperature of 1000° C. or more.

In the purification method of the present invention, the silica powderin a fluid state is positioned in the magnetic field region. The silicapowder in the fluid state positioned in the magnetic field regiongenerates the electric field based on the Fleming's rule by moving thepowder, and voltage is applied to the silica powder. Thereby, the ionicimpurity components in the silica powder are induced by the electricfield, and diffused onto the powder surface. Therefore, the impuritycomponents are easily reacted with the purification gas so that the highpurification effect can be obtained in a short time.

In order to freely move the silica powder in the magnetic field region,the silica powder in the magnetic field region is kept in a fluid state.In addition, the fluid state of the present invention includes not onlya state for generating convection but also a state including a floatingstate in which the silica powder can be freely moved.

The intensity of the magnetic field is suitably 10 gausses or more. Ifthe intensity of the magnetic field is less than 10 gausses, the effectfor accelerating diffusing of the impurity components is low, and thepurification effect is not increased sufficiently. More preferably, theintensity of the magnetic field is 10 gausses or more to 150 gausses orless. The good effect for refining can be obtained in this range.

Further, a reaction temperature at the time of contacting the fluidizedsilica powder to the purified gas is preferably from 1000° C. or more to1300° C. or less. If the reaction temperature is less than 1000° C., theimpurity components contained in the silica powder is not ionic-moved,so that the diffusing speed of the impurity components to the powdersurface is hardly increased. If the reaction temperature is more than1300° C., the production cost becomes high since carrying out at thehigh temperature. In the purification method of the present invention,the excellent purification effect can be obtained at the temperature ofabout 1200° C.

In order to diffuse and move the impurity components contained in thesilica powder onto the powder surface, it is necessary to fluidize thesilica powder and position in the magnetic field. In order to fluidizethe silica powder and position in the magnetic field, for example, asilica powder is filled in a fluidized bed having a magnetic fieldforming means, and air or inert gas is blown into the fluidized bed soas to fluidize the silica powder, and thereby, the magnetic field isformed in the fluidized bed. Further, when a cyclone-shaped containerhaving a magnetic field forming means is used, a silica powder is blowninto the container together with air or inert gas so as to fluidize thesilica powder, and the magnetic field can be applied. In addition, thepurification gas can be used for fluidizing the silica powder.

As for the purification gas, a gas enables to gasify the impuritycomponents when reacting on the powder surface is used. Moreparticularly, for example, halogen gas such as gaseous chlorine or thelike, and hydrogen halide gas such as hydrogen chloride gas or the likecan be used. The purification gas is introduced into the silica powderfluidized in the magnetic field, or the silica powder is fluidized inthe magnetic field by the purification gas. Thereby, diffusing of theimpurity components contained in the silica powder is accelerated so asto move the impurity components onto the powder surface. As a result ofthis, the impurity components are contacted and reacted with thepurification gas on the powder surface so as to become a chloride gasand the like and removed.

According to the purification method of the present invention, apurified silica powder having remarkable few impurity components can beobtained by the purification in a short time. Among the impuritycomponents, an alkali impurity component has the highest purificationeffect since being very often ionic-moved at a high temperature.Especially, it is excellently effective to remove Li which has a highionicity.

When the purification method of the present invention is carried out,for example, the following purification apparatus can be used, that is,a purification apparatus including: a fluidized bed for fluidizing thesilica powder, or a reaction container for receiving the fluidizedsilica powder; a means for introducing a purified gas into the fluidizedbed or the reaction container; a means for heating in the fluidized bedor the reaction container at from 1000° C. to 1300° C.; and a means forforming a magnetic field of 10 gausses or more in the fluidized bed orthe reaction container.

As the apparatus in the present invention, the fluidized bed may possessa function of the reaction container. For example, vertical andcylindrical type fluidized bed is used, a lower part of fluidized bed isdivided by a floor plate having many air hole, the silica powder isfilled on the upper side of the floor plate, the purification gas in-letport is provided at the lower side of the floor plate, and the gasout-let port is provided on the upper side of the fluidized bed. On theother hand, the heater is provided on the outer periphery of thefluidized bed and the means for forming the magnetic field is providedon an outside of the heater. The silica powder in the fluidized bed ismade to be fluidizing state by the purification gas and the inside ofthe fluidized bed is heated from 1000° C. or more to 1300° C. or lessand the magnetic field is formed 10 Gauss or more by the means forforming the magnetic field. Then, the impurity in the silica powder isreacted with the purification gas so as to be vaporized. The generatedgases by the reaction are exhausted from the fluidized bed with theun-reacted purification gas.

In addition, before introducing the purification gas, the following gasflow is possible. That is, air is introduced with silica powderbeforehand through the purification gas in-let port so as to fluidizethe silica powder, and thereafter, the purification gas is introduced inthe fluidized bed instead of air, or the purification gas is introducedwith air in the fluidized bed.

As for the reaction conditions, for example, the 1% to 15% concentrationof purification gas can be contacted with the silica powder at 1000° C.to 1300° C. for 60 min. to 90 min.

Further, the cyclone-shaped container can be used instead of theabove-described apparatus. In the container, the temperature is set to1000° C. to 1300° C., and a magnetic field of 10 gausses or more isformed in a region including the inside of the container. Silica powderis introduced into the container together with air so as to fluidize thesilica powder. After that, the purification gas is blown into thecontainer so as to react to the impurity components of the silicapowder. The generated gases by the reaction are exhausted from thereaction container together with un-reacted purification gas.

An example of an apparatus for carrying out the purification method ofthe present invention is illustrated in FIG. 1. As illustrated in FIG.1, a purification apparatus 10 includes a vertical and cylindricalfluidized bed 11, and a heater 12 surrounding the fluidized bed 11.Further, a pair of magnets 13 is provided on both sides of the fluidizedbed 11 including the heater 12. The fluidized bed 11 is formed by aquartz tube, and includes an inducing port for the purification gas at abottom part thereof, and an exhaust port at an upper part thereof.Further, the fluidized bed 11 includes a bottom plate 14 inside thereof,and many vent holes are provided at the bottom plate 14.

When the purification gas is introduced from the bottom part of thefluidized bed 11, the gas flows toward the upper part of the fluidizedbed 11 through the vent holes of the bottom plate 14 so as to fluidize asilica powder 15 stored on the upper side of the bottom plate 14, andthen, exhausted from the exhaust port at the upper part of the fluidizedbed. On the other hand, the inside of the fluidized bed is heated atabout 1200° C. by the heater 12, and the magnetic field of 10 gausses ormore is formed in the fluidized bed by the magnets 13.

As for the silica powder kept to have the fluidized state by thepurification gas, the silica powder is moved in the magnetic field of 10gausses or more so as to generate an electric field, so that voltage isapplied to the silica powder. Thereby, ionic impurity components in thesilica powder, for example, lithium ion or the like are induced onto thepowder surface by the electric field, and contacted and reacted with thepurification gas at a high temperature of about 1200° C. so as to formchloride to be gasified. The gasified chloride is removed from thesilica powder.

EXAMPLE

A silica powder was subjected to a purification treatment by the stepsof: taking 20 kg silica powder having an average powder diameter of 220μm into a quartz reaction container having an inner diameter of φ4250mm; forming a fluid layer using air as carrier gas; forming a magneticfield in a fluid region; and inducing purification gas into thecontainer at a high temperature (Example). In addition, a silica powderwas subjected to the purification treatment by inducing the purificationgas without forming the magnetic field in the fluid region (Comparisonexample). The effects by these treatments were shown in Table 1 incomparison. According to the example of the present invention, when thetreatment time was 1 hour, each alkali metal content was 0.15 ppm orless, and partially 0.05 ppm or less. Especially, Li was largelyremoved. On the other hand, alkali metal contents of the comparisonexample were 0.3 ppm or more, and especially, Li was hardly removed.

TABLE 1 Magnetic Impurity Components Purification Gas TreatmentTreatment Intensity (ppm) Kinds Concentrations Temperature Time (gauss)Na K Li Before — — — — — 2.4 0.71 4.2 Treatment Example 1 Cl₂ 2% 1150°C. 1 hour 20 0.09 0.07 0.12 Example 2 Cl₂ 0.5%   1150° C. 1 hour 1000.09 0.08 0.10 Example 3 Cl₂ 5% 1150° C. 1 hour 100 0.07 0.06 0.06Example 4 HCl 2% 1150° C. 1 hour 100 0.04 0.06 0.06 Example 5 Cl₂ +  1 + 0.2% 1150° C. 1 hour 100 0.04 0.04 0.04 HCl Example 6 Cl₂ + 5 + 5%1150° C. 1 hour 100 0.05 0.05 0.04 HCl Example 7 Cl₂ + 5 + 5% 1150° C. 1hour 100 0.02 0.04 0.05 HCl Example 8 Cl₂ + 5 + 5% 1260° C. 1 hour 500.01 0.03 0.02 HCl Comparison Cl₂ 5% 1150° C. 1 hour No 0.36 0.41 4.11example 1 Comparison Cl₂ 5 + 5% 1150° C. 1 hour No 0.33 0.30 4.06example 2 Comparison Cl₂ + 20 + 60% 1150° C. 1 hour No 0.26 0.28 4.01example 3 HCl

POSSIBILITY OF APPLICATION FOR INDUSTRY

The treatment method of the present invention has high purificationeffect at a temperature of 1000° C. to 1300° C., which is lower than anaverage treatment temperature of the conventional gas purificationmethods. Thus, there is an advantageous that an energy cost is low.Further, if a halogen gas is used as the purification gas, there is nodanger of explosion, so that an operation can be carried out safety.

1. A purification method of a silica powder comprising: making a silicapowder into a fluid state; contacting a purification gas to the silicapowder in the fluid state at high temperature so as to remove impuritycomponents of the silica powder, wherein the silica powder in the fluidstate is positioned in a magnetic field area, and wherein the silicapowder is contacted with the purification gas while applying voltage tothe silica powder by an electric field which is generated by moving thesilica powder.
 2. The purification method of a silica powder accordingto claim 1, wherein the silica powder in the fluid state is positionedin a magnetic field area of 10 gausses or more, and contacted with thepurification gas at a temperature of 1000° C. or more.
 3. Thepurification method of a silica powder according to claim 1, wherein thepurification gas contains any one or both of halogen gas and hydrogenhalide gas.
 4. The purification method of a silica powder according toclaim 1, wherein the purification temperature is from 1000° C. or moreto 1300° C. or less.
 5. A purification apparatus for a silica powdercomprising: a fluidized bed configured to fluidize the silica powder, ora reaction container configured to receive the fluidized silica powder,and a means for introducing a purification gas into the fluidized bed orthe reaction container; a means for heating in the fluidized bed or thereaction container at from 1000° C. to 1300° C.; and a means for forminga magnetic field of 10 gausses or more in the fluidized bed or thereaction container.
 6. A purification apparatus according to claim 5;wherein the fluidized bed possesses a function of the reactioncontainer, a lower part of a vertical and cylindrical type fluidized bedis divided by a floor plate having many air holes, the silica powder isfilled on the upper side of the floor plate, a purification gas in-letport is provided at the lower side of the floor plate, and a gas out-letport is provided on the upper side of the fluidized bed; wherein aheater is provided on an outer periphery of the fluidized bed and themeans for forming the magnetic field is provided outside of the heater;wherein the silica powder in the fluidized bed is made to be in afluidizing state by the purification gas; wherein the inside of thefluidized bed is heated from 1000° C. or more to 1300° C. or less; andwherein a magnetic field of 10 Gauss or more is formed by the means forforming the magnetic field.
 7. A purified silica powder, whereinimpurity components are removed by the purification method according toclaim 1.